ABSTRACT The Biology Core provides technical support and generates advanced biological reagents that support mechanistic and structural studies of HIV-1 replication and transmission. Capabilities in virology include access to standard reporter viruses and vectors, infectivity assays, custom fluorescently- and luciferase-labeled viruses for imaging in tissues and animals1-7, protocols for selecting resistance to anti-retroviral drugs and restriction factors8, and the ability to purify HIV-1 virions and cores for biochemical and structural studies.9-12 Cell biology resources include infectable cell lines and primary cells, models for viral latency13-15, the ability to deplete and characterize host factors using RNA interference and CRISPR/Cas9 approaches16-18, and the generation of cell lines that express exogenous and/or fluorescently-labeled proteins, as well as capabilities in proteomics and advanced imaging. Humanized mouse models19-24 are also used, together with labeled replicating viruses, to study replication and dissemination in vivo.4 Finally, viral replication and cell biology can be studied in several primate models, including SHIV-infected early foci in infected macaque tissues, and human mucosal cells and tissues for studies of HIV-1 transmission and restriction.25-31